Flexible polyurethane foam is used for bedding and upholstered furniture due to its durability, lack of odor, non-allergenic properties, ease of cleaning, and resistance to dry-cleaning solvents, oils, and perspiration. However, ordinary flexible polyurethane foam can readily ignite because of its open cell structure, which allows the oxygen required for combustion to penetrate below the surface of the foam. Once ignited, flexible polyurethane foam tends to burn vigorously because of its very large surface area per unit weight. These risks have lead to the implementation of safety standards for industries that use polyurethane foam.
In order to meet safety standards, considerable efforts have been made to provide polyurethane foams with satisfactory flame retardancy. Most flexible polyurethane foams are produced by a condensation reaction between a polyether polyol and an isocyanate in the presence of foam forming agents. When these compounds are mixed together, liberated carbon dioxide gas acts as the blowing gas to make the material into foam. One approach to produce foams with satisfactory flame retardancy has been to add reactive or non-reactive flame-retardant as a part of the foam producing process. Phosphorus and/or halogenated compounds, borates, aluminum trihydrate, melamine, expandable graphite, and many other flame-retardants have been used in the foam making process. Another approach to make flame retardant foam is to post-treat the foam with flame-retardants after the foam has been produced.
Silicone foam is produced by a condensation reaction between a siloxane polymer containing silanol (Si—OH) groups and crosslinkers containing silane (Si—H) groups in the presence of a catalyst. When these compounds are mixed and reacted together, the formation of siloxane linkages (Si—O—Si) occurs, liberating hydrogen gas, which acts as the blowing agent to make the material into foam. Because of its high silicone content, silicone foam is typically less flammable than flexible polyurethane foam.
The most widely used silicones are based on polydimethylsiloxanes (PDMS). Tyagi, Yilgor, McGrath and Wilkes, Polymer, 1984, 25, 1807 reported that the characteristics of these siloxanes such as very low intermolecular forces, ease of rotation, and relatively long and fairly strong Si—O bond enable these polymers to exhibit flexibility, thermal stability, and properties which are fairly constant over a wide range of temperature. Silicone polymers in general are also known to have unique and useful properties such as low surface energy, low glass transition temperature, and high gas permeability. Robb and Ann, Acad. Sci. 1968, 146, 119 reported that silicone polymer is 10 times more permeable to oxygen than natural rubber and low-density polyethylene and 100 times greater than butyl rubber and nylon. Silicone polymers, including polydimethylsiloxane when not crosslinked, are widely used in the fields of cosmetics, food processing and various medical applications.
Siloxane-modified polyurethanes have a wide range of applications since their properties can be tailored by variations of their components. Siloxane-modification of polyurethanes has shown microphase segregation producing a silicone-rich soft segment in polyurethane elastomers. According to Couchman (Macromolecules, 1978, 11, 1156) and Camberlin, and Pascault (J. Polym. Sci., Polym. Phys. Edn., 1984, 22, 1835), one of the reasons for this phase separation is the incompatibility of the soft segment (solubility parameter, δ=7.46 cal1/2 cm−3/2 mol−1) with polar hard segment (δ=13.2). This unique rearrangement process depends on various factors such as polydimethylsiloxane length, siloxane content and the nature of the contacting surface. Tezuka, Kazama and Imal, J. Chem. Soc. Faraday Trans., 1991, 87(1), 147 reported that the top surface of a block copolymer can be completely covered with the polydimethylsiloxane in the dry state and the thickness of the top layer ranged from 20-100 A° depending on the siloxane block length and siloxane content. When the contacting surface changed from dry to aqueous, a surface rearrangement occurred producing a polyurethane-like surface. The structure and the orientation behavior of these polymers were studied by means of infrared dichroism, small angle light scattering, and differential scanning calorimetry and it was found that the incorporation of siloxane moiety in the main chain reduced the crystallization capability of the soft segments. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), ESCA, and FT-IR studies of a large number of silicone modified polyurethane elastomers revealed that these block co-polymers contained a silicone rich surface. Nelson, Jayakody, and Sorathia “Silicone Modified Polyurethanes”, Proceedings, The 8th Annual BCC Conference on Flame Retardancy, Stamford, Conn. (1997) reported utilizing difunctional polydimethylsiloxanes both silanol terminated (Si—OH) and aminoalkyl terminated, to increase fire-retardancy of elastomeric polyurethanes. Cone calorimetric data showed polyurethane elastomers prepared using aminopropyl dimethyl terminated PDMS gives lower peak heat release rates than silanol terminated PDMS. They have identified some formulations with aminopropyl dimethyl terminated PDMS which gave peak heat release rates as low as 300 kW/m2 compared to polytetramethylene ether glycol modified polyurethane elastomers (2577 kW/m2) at 25 kW/m2 exposure. Jayakody, Nelson, Sorathia and Lewandowski “A Cone Calorimetric Study of Flame Retardant Elastomeric Polyurethanes Modified with Siloxanes and Commercial Flame Retardant Additives”, J. Fire Sci. Vol. 16, 1998, 351-382 showed that the replacement of polytetramethylene ether glycol from MDI based polyurethane elastomers with isobutylmethylamine terminated polydimethylsiloxanes showed a 89% reduction of peak heat release rate (261 kW/m2) compared to the polytetramethylene ether glycol based system (2435 kW/m2) at 25 kW/m2 exposure.
The above discussion shows that the incorporation of siloxane block into the backbone of polyurethane elastomers yields a significant improvement on the flame retardancy of the polymers. A practical flexible foam including a siloxane moiety would be desirable in the art. The primary object of this invention, therefore, is to provide a new opened cell flexible silicone foam.